大小写切换改为原地更新字符，不重建页面

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

LearnEnglish/LearnEnglish/Models/Quiz.swift

@@ -51,6 +51,27 @@ enum QuizGenerator {
         }
     }
 
+    static func recase(_ questions: [QuizQuestion], toUpper: Bool) -> [QuizQuestion] {
+        questions.map { q in
+            let word = q.word
+            let text = toUpper ? word.word.uppercased() : word.word.lowercased()
+            let recased = Word(categoryId: word.categoryId, word: text, phonetic: word.phonetic,
+                               meaning: word.meaning, example: word.example, exampleMeaning: word.exampleMeaning)
+            let blanked = q.blankedWord.map { ch -> String in
+                ch == "_" ? "_" : ch.uppercased()
+            }.joined()
+            let blankedWord = toUpper ? blanked.uppercased() : blanked.lowercased()
+            return QuizQuestion(
+                word: recased,
+                prompt: q.prompt,
+                options: q.options,
+                answer: text,
+                blankedWord: blankedWord,
+                blankPositions: q.blankPositions
+            )
+        }
+    }
+
     private static func promptText(_ word: Word, _ mode: QuizMode) -> String {
         switch mode {
         case .enToZh: return word.word

LearnEnglish/LearnEnglish/Views/QuizViewController.swift

@@ -425,15 +425,8 @@ final class QuizViewController: UIViewController {
         isUppercase.toggle()
         UserDefaults.standard.set(isUppercase, forKey: "spelling_uppercase")
         updateCaseButton()
-        selectedOption = nil
+        questions = QuizGenerator.recase(questions, toUpper: isUppercase)
-        let words = config.words.map { word in
+        spellingView.updateCase(toUpper: isUppercase)
-            let text = isUppercase ? word.word.uppercased() : word.word.lowercased()
-            return Word(categoryId: word.categoryId, word: text, phonetic: word.phonetic,
-                        meaning: word.meaning, example: word.example, exampleMeaning: word.exampleMeaning)
-        }
-        questions = QuizGenerator.makeQuestions(mode: config.mode, words: words)
-        showQuestion()
-        spellingView.activate()
     }
 
     private func updateCaseButton() {

LearnEnglish/LearnEnglish/Views/SpellingInputView.swift

@@ -133,6 +133,20 @@ final class SpellingInputView: UIView, UITextFieldDelegate {
         hiddenField.inputAccessoryView = nil
     }
 
+    func updateCase(toUpper: Bool) {
+        chars = chars.map {
+            guard $0 != "_" else { return $0 }
+            return toUpper ? $0.uppercased() : $0.lowercased()
+        }
+        filledBlanks = filledBlanks.map {
+            $0.isEmpty ? $0 : (toUpper ? $0.uppercased() : $0.lowercased())
+        }
+        for (index, box) in boxViews.enumerated() where chars[index] != "_" {
+            (box.viewWithTag(100) as? UILabel)?.text = chars[index]
+        }
+        refreshBoxes()
+    }
+
     func showResultState(correct: Bool) {
         let color = correct ? Theme.Color.correct : Theme.Color.wrong
         for position in blankPositions {